17 billion Earth-size planets?

LONG BEACH, Calif. — Astronomers hunting for Earth-like planets now have many places to look. A new estimate released Monday suggested the Milky Way galaxy is home to at least 17 billion similar planets.

It doesn’t mean all are potentially habitable, but the sheer number of Earth-size planets is a welcome starting point in the search for worlds like our own.

Scientists have yet to find a twin Earth — one that’s not only the right size but also located in the so-called Goldilocks zone, a place that’s not too hot and not too cold where water might exist in liquid form.

Two independent groups came up with the new estimate after a fresh analysis of data gathered by NASA’s Kepler spacecraft, which was launched in 2009. One team was from the Harvard-Smithsonian Center for Astrophysics; the other from the University of California, Berkeley and University of Hawaii.